The purpose of this study is to test the hypotheses that BMC of the proximal femur, lumbar spine, and distal radius can be improved in postmenopausal women through 1) weight-bearing exercise training, 2) non-weight-bearing exercise training, and 3) passive weight-bearing activity. Sedentary Caucasian women 62-72 yr of age will be recruited over 36 mo at a rate of 2 to 3 subjects per mo. Subjects eligible to participate in the exercise program will be randomly assigned to weight-bearing exercise, non-weight-bearing exercise, and non-exercise control groups. The exercise program will consist of 3 mo of flexibility exercise followed by 9 mo of weight-bearing (walking, jogging, stair climbing) or non-weight-bearing (cycling, roving, weightlifting) exercise. A cross-over study design will be used. After 9 mo, the subjects who were doing weight-bearing exercise will switch to non-weight-bearing exercise, while those in the non-weight-bearing exercise group will convert to weight-bearing exercise, for an additional 9 mo of training. The effect of passive weight-bearing on bone mass will be studied in the non-exercise control group; after completion of the 12-mo control period, the subjects will be provided with vests containing weights adjusted from 10 to 304 body weight. The weighted vests will be worn for 1 hr daily for 9 mo during routine daily activities. Bone mass of the proximal femur and lumbar spine will be assessed by dual energy radiography (DER) at baseline and at approximately 4.5-month intervals throughout the period of intervention. Bone mass of the distal radius, which is not involved in the weight-bearing exercise, will be measured by single photon bone densitometry to assess systemic, as opposed to localized, affects of exercise on bone formation. Plasma and urine chemistries will be obtained to gain information regarding possible mechanisms underlying the observed responses.